Tài liệu Chapter 9 - Ethernet CCNA Exploration 4.0 pptx

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e Identify the basic characteristics of network media used in

Ethernet

° Describe the physical and data link features of Ethernet

e Describe the function and characteristics of the media access

control method used by Ethernet protocol

e Explain the importance of Layer 2 addressing used for data

transmission and determine how the different types of

addressing impacts network operation and performance

° Compare and contrast the application and benefits of using

Ethernet switches in a LAN as apposed to using hubs

e Explain the ARP process

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| Transport | Ethernet is defined by Data Link

layer and Physical layer protocols

| Network |

Data Link LL€ 802.2

802.3 Physical

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IEEE (Electrical and Electronics Engineers) Standards

The first LAN is the original version of Ethernet Robert Metcalfe and his coworkers at Xerox designed it more than thirty years ago The first Ethernet standard was published in 1980 by a consortium of Digital

Equipment Corporation, Intel, and Xerox (DIX).It was released as an open standard The first Ethernet standard products were sold in the early 1980s

In 1985, the IEEE standards committee for Local and Metropolitan

Networks published standards for LANs These standards start with the number 802, and 802.3 is for Ethernet To compare to the International standards Organization (ISO) and OSI model, the IEEE:802.3

standards had to address the needs of Layer 1 and\the lower portion of Layer 2 of the OSI model As a result, some small'modifications to the Original Ethernet standard were made in 80233

Ethernet operates in the lower two layers of the OSI model: the of the Data Link layer and the Physical layer

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Layer 2 Addresses Layer 1 Limitations

Layer 1 Limitations Layer 2 Functions

Cannot communicate with upper

layers Connects to upper layers via Logical

Link Control (LLC)

Uses addressing schemes to identify

devices

Cannot identify devices

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BACHKHOd NETWORKING ACADEMY

Logical Link Control (LLC)

« Makes the connection with the upper layers

« Frames the Network layer packet

5 Identifies the Network layer protocol

« Remains relatively independent of the physical equipment

Logical Link Control Sublayer 802.3 Media Access Control

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* Data Encapsulation

* Frame delimiting + Addressing

* Error detection

* Media Access Control

¢ Control of frame placement on and off the media

+ Mediarecovery

e Media Access Control (MAC) is the lower Ethernet sublayer of,the Data Link layer MAC is implemented by hardware, typically-in the computer Network Interface Card (NIC)

e The Ethernet MAC sublayer has two primary responsibilities:

— Data Encapsulation

— Media Access Control

° Logical Topology: all the nodes (devices) inthat network segment share the medium This requires examining the addressing in the

frame provided by the MAC address, and using of CSMA/CD

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BACHKHOA NETWORKING ACADEMY

Ethernet switch Hoc vién mang Bach khoa - Website: www.bkacad.com

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° Most of the traffic on the Internet originates and ends with Ethernet connections Since its inception in the 1970s,

Ethernet has evolved to meet the increased demand for

high-speed LANs When optical fiber media was

introduced, Ethernet adapted to this new technology to

take advantage of the superior bandwidth and low error

rate that fiber offers Today, the same protocol that

transported data at 3 Mbps can carry data at 10 Gbpsy

e The success of Ethernet is due to the following factors:

— Simplicity and ease of maintenance

— Ability to incorporate new technolegies

— Reliability

— Low cost of installation and upgrade

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and collision detection

techniques were adapted

from the Alohanet radio

network

Shared bus topology

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lIlll BACHKHOA NETWORKING ACADEMY Early Ethernet Media and Topology

Topology Physical: Bus Logical: Bus 8 5

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e Early Ethernet Media: Coaxial cable

— Logical and physical bus topology

— 10BASE5, or Thicknet, used a thick coaxial that allowed for cabling distances of up to 500 meters before the signal required a repeater

— 10BASE2, or Thinnet, used a thin coaxial cable that was smaller in diameter and more flexible than Thicknet and allowed for cabling

distances of 185 meters

° Now, it was replaced by UTP cables

— The UTP cables were easier to work with, lightweight, and Jess

expensive

— Physical topology was a star topology using hubs::'Hubs

concentrate connections Any single cable to-fail without disrupting the entire network However, repeating.the frame to all other ports did not solve the issue of collisions

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Printer0

Server-PT

Legacy Ethernet Server0 PC0

In 1OBASE-T networks, typically using a hub Thịs created a'shared

media Only one station could successfully transmit at a1ime:.lialí-

duplex communication

More devices, more collisions

Using CSMA/CD to manage collisions, with littlevor no impact on

performance As the number of devices and Subsequent data traffic

increase, however, the rise in collisions can have a significant impact

on the user's experience

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Printer-PT PrinterO

2960-

24TT Switch

0

Server-PT

Current Ethernet Server poo

° 1OOBASE-TX Ethernet Switches replace hubs

° Switches can control the flow of data by isolating each portand sending

a frame only to its proper destination (if the destinationiskKnewn), rather than send every frame to every device

e The switch reduces or minimizes the possibility’of collisions

° Support full-duplex communications (transmit and receive signals at the

same time)

1Gbps Ethernet and beyond

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The applications tax even the

most robust networks For Moving Ethernet to 1 Gbps and Beyond

example, the increasing use of aT

multimedia services requires q7

connections that are faster than

100 Mbps Ethernet

New networking services

Some of the equipment and

cabling in modern, well-designed &

and installed networks may be | q7

capable of working at the higher ct"

speeds with only minimal

upgrading This reduces the total

cost

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®

Gigabit Ethernet Gigabit Ethernet technology is applied beyond the enterprise

LAN to MAN and WAN-based networks

WAN

Metropolitan- area Network

KH: Sao

LAN

The increased cabling distances enabled by the use of fiber-optic cable in Ethernet-based networks has resulted in a blurring of the distinction between LANs and WANs Ethernet was

initially limited to LAN cable systems within single

buildings, and thenvextended

to between buildingsx|It can now be applied.across a city

in whatis known as a Metropolitan Area Network (MAN)

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Ethernet Frame

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and Performance _ ee

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e The Frame — Encapsulating the Packet

Comparison of 802.3 and Ethernet Frame Structures and Field Size

Field size in

bytes

Preamble Start of Frame Destination Source Length/ 802.2 Header and Frame Check

delimiter Address Address Type Data Sequence

Sequence

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«The Preamble is used for

timing synchronization in the asynchronous 10 Mbps and slower implementations of

107101011 Ethernet Faster versions of

Preamble Destination | Source Type Data Frame

Address Address Check

Sequence

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Ethernet are synchronous, and this timing information is

redundant but retained for compatibility

«The Destination Address field contains the MACwdestination address It canbe unicast, multicasi(group),or broadcast (all nodes)

«|he source address is generally the unicast address

of the transmitting Ethernet node (can be virtual entity — roup or multicast)

d.com

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Preamble Start of Destination | Source Length’ 802.2 Header | Frame Check

Frame Address Address Type and Data Sequence

Preamble Destination Source Type Data Frame

Address Address Check

«The type value specifies the upper-layer protocol to receive the data after Ethernet

processing is completed

«The length indicates the number of bytes of data that follows this field (so contents of the Data field are decoded per the protocol indicated)

eThe maximum transmission unit (MTU) for Ethernet,is 500

octets, so the data should not exceed that-size

e-Ethernetrequires that the frame

be motlesssthan 46 octets or more than 1500 octets (Pad is required if not enough data)

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The MAC Address—Addressing in Ethernet

All Ethernet nodes share the media

To receive the data sent to it, each node needs a unique address

Shared Media (Multiple Access)

| Yes, that frame |

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Organizational Unique Identifier Vendor Assigned

(OUI) (NIC Cards, Interfaces)

‘Sometimes referred to as burned-in addresses (BIA) because they are

burned into read-only memory (ROM) and are copied into random-access memory (RAM) when the NIC initializes

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Physical Address

Dhep Enabled -s

Autoconfiguration Enabled

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DACP S@rver ssa iv Ss www GS

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: Yes : Yes

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° Another Layer of Addressing

Different Layers of Addressing

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mm || /UllIlUIUUWUU BACHKHOA NETWORKING ACADEMY Data Link Layer

° OSI Data Link layer (Layer 2) physical addressing,

implemented as an Ethernet MAC address, is used to

transport the frame across the local media Although

providing unique host addresses, physical addresses are non-hierarchical They are associated with a particular

device regardless of its location or to which network it is

connected

° These Layer 2 addresses have no meaning outside the

local network media A packet may have to.raverse a

number of different Data Link technologies inslocal and

wide area networks before it reaches ‘its.destination A

source device therefore has no knowledge of the

technology used in intermediate and destination networks

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° Network layer (Layer 3) addresses, such as IPv4

addresses, provide the ubiquitous, logical addressing that

is understood at both source and destination To arrive at its eventual destination, a packet carries the destination

Layer 3 address from its source However, as it is framed

by the different Data Link layer protocols along the way,

the Layer 2 address it receives each time applies only to that local portion of the journey and its media

In short:

° The Network layer address enables the packet to be

forwarded toward its destination

° The Data Link layer address enables the packet to be

carried by the local media across each segment

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| | | BACHKHOA NETWORKING ACADEMY

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Ethernet Media Access Control

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Media Access Control in Ethernet

Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

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detected

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| JAM JAM JAM JAM JAM JAM |

Jam signal issued

3 y ZR

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This network with 35 hosts and 5 hubs is a single

collision/broadcast domain When one host or

server transmits a message, all other devices in

the domain receive the message

More importantly, only one device in the entire

network can send data at any one time

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Ethernet Delay (Latency)

An Ethernet frame takes a measurable time to travel from the _-

sending device to the receiver Each intermediary device

contributes to the overall latency

e The electrical signal that is transmitted takes a certain amount of time (latency) to propagate (travel) down the cable Each“hub or repeater in the signal's path adds latency as it forwards the bits from one port to the next

e This accumulated delay increases the collisions,because a

listening node may transition while the hub or repeater is processing the message Because the signal had not reached this node while it was listening, it thought that the media was

available This condition often results in collisions

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10 Mbps and slower Ethernet use the first

64 bits of the frame Preamble to synchronize the receiver

° Ethernet 10Mbps and slower are asynchronous

° Ethernet 100Mbps and higher are.synchronous However, for compatibility reasons, the Preamble and Start Frame

Delimiter (SFD) fields are still present

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Ethernet Slot and Bit Times Slot time =A+B

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first bytes sent last bytes sent first bytes sent last bytes sent

e Bit Time: For each different media speed, a period of time is required for a bit to be placed and sensed on the media This period of time is referred to as the bit time

° Slot Time: In half-duplex Ethernet, where data can only travel in-one

direction at once, slot time becomes an important parameter in

determining how many devices can share a network,.For all Soeeds of Ethernet transmission at or below 1000 Mbps, the‘standard describes how an individual transmission may be no smaller.than the slot time

e Interframe Spacing: this time is measured fronvthe last bit of the FCS

field of one frame to the first bit of the Preamble of the next frame

Tiêu đề	Ethernet
Tác giả	Robert Metcalfe, Xerox
Trường học	Học viện mạng Bách khoa
Thể loại	Bài giảng

Định dạng
Số trang	94
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